1. Field of the Invention
The present invention relates to a display device equipped with a sync signal reproducing circuit for a composite video signal and, more particularly, to a sync signal reproducing circuit incorporated in a display device for reproducing horizontal and vertical sync signals from luminance signals separated from a composite-video signal externally applied in one of a TV broadcasting mode and a super VHS (S-VHS) mode in order to select signal processing of one of a composite video signal and a VGA video signal for a variable visual display on a screen.
2. Discussion of Related Art
As the performance and scale of microprocessors progress, computer systems have become increasingly sophisticated in processing a variety of information data, such as text, sounds, graphics, animation, movie, and so forth. Such computer systems are known as multimedia computers. In order to perform multimedia function, hardware such as high performance video card, sound card, TV/radio card, and modem must be installed in the computers.
Display devices such as a CRT type of monitor, must process separately a VGA video signal received from a video card installed in the computer system and a composite video signal received from a different source (e.g., TV/radio card) in either a TV broadcasting mode or a super VHS (S-VHS) VHS) mode for a visual display on a screen. For this reason, if a composite video signal processing circuit is built into the display device and in order to selectively output a composite video signal and a VGA video signal, a sync signal reproducing circuit is necessarily required to isolate a sync signal from a luminance signal separated from the composite video signal so that the composite video signal and the VGA video signal can be selected for a visual variable display on a screen.
Accordingly, it is therefore an object of the present invention to provide a sync signal reproducing circuit incorporated in a display device for reproducing a sync signal from a luminance signal separated from a composite video signal.
It is also an object to provide a sync signal reproducing circuit incorporated in a display device of a multimedia computer system for reproducing a sync signal from a luminance signal separated from a composite video signal externally applied from one of a TV broadcasting mode and a super VHS (S-VHS) mode for effective selection of a VGA video signal or the composite video signal for a variable visual display on a screen.
These and other objects of the present invention can be achieved by a sync signal reproducing circuit incorporated in a display device which comprises: a channel selector for receiving a first composite video signal and a second composite video signal output from a composite video signal input stage, and also receiving a composite video signal selection signal output from a microcomputer, to thereby selectively output the first and second composite video signals; a digital computer (D-COM) filter for receiving the composite video signal selected by the channel selector, and separately outputting its chrominance signal and luminance signal; and a chroma circuit for receiving the chrominance signal and luminance signal of the composite video signal output from the D-COM filter, and thus reproducing the chrominance signal and separating horizontal and vertical sync signals from the luminance signal.
In accordance with another aspect of the present invention, a sync signal reproducing circuit for a composite video signal comprises: a channel selector for receiving a first composite video signal and a second composite video signal output from a composite video signal input stage, and also receiving a composite video signal selection signal output from a microcomputer, to thereby selectively output the first and second composite video signals; a D-COM filter for receiving the composite video signal selected by the channel selector, and separately outputting its chrominance signal and luminance signal; a chroma circuit for receiving and reproducing the chrominance signal of the composite video signal output from the D-COM filter; a first multivibrator for receiving the luminance signal of the composite video signal output from a chroma IC section, to thereby output a horizontal sync signal; and a second multivibrator for receiving the luminance signal of the composite video signal output from the chroma circuit, to thereby output a vertical sync signal.
The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example.